From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4B09DC43331 for ; Mon, 30 Mar 2020 13:51:47 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 96670206CC for ; Mon, 30 Mar 2020 13:51:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="TVppmMOS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 96670206CC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-18298-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 11821 invoked by uid 550); 30 Mar 2020 13:51:39 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 11789 invoked from network); 30 Mar 2020 13:51:38 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585576286; bh=shRxHPO6TNubPsJ8Kjm+VBtKtgZ9LoE0ypNOsjrhlXw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TVppmMOSXAOdk3sfXijAOW160toaPEfSbfuCM5nMPwj/I3zOVURZQDOSEZuSPsYYy kqP/py9AFaPG8DnYkTKU1srHzS+4+sedlU3OhdM4pJaipPpH+n4oNZtKNI7ilOgM3T 9HiPi2kWUIqDGyNDy4oebEE3SwMtrpR/lsMZf0PE= Date: Mon, 30 Mar 2020 14:51:21 +0100 From: Will Deacon To: Ard Biesheuvel Cc: linux-arm-kernel@lists.infradead.org, kernel-hardening@lists.openwall.com, catalin.marinas@arm.com, mark.rutland@arm.com Subject: Re: [RFC PATCH] arm64: remove CONFIG_DEBUG_ALIGN_RODATA feature Message-ID: <20200330135121.GD10633@willie-the-truck> References: <20200329141258.31172-1-ardb@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200329141258.31172-1-ardb@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) On Sun, Mar 29, 2020 at 04:12:58PM +0200, Ard Biesheuvel wrote: > When CONFIG_DEBUG_ALIGN_RODATA is enabled, kernel segments mapped with > different permissions (r-x for .text, r-- for .rodata, rw- for .data, > etc) are rounded up to 2 MiB so they can be mapped more efficiently. > In particular, it permits the segments to be mapped using level 2 > block entries when using 4k pages, which is expected to result in less > TLB pressure. > > However, the mappings for the bulk of the kernel will use level 2 > entries anyway, and the misaligned fringes are organized such that they > can take advantage of the contiguous bit, and use far fewer level 3 > entries than would be needed otherwise. > > This makes the value of this feature dubious at best, and since it is not > enabled in defconfig or in the distro configs, it does not appear to be > in wide use either. So let's just remove it. > > Signed-off-by: Ard Biesheuvel > --- > arch/arm64/Kconfig.debug | 13 ------------- > arch/arm64/include/asm/memory.h | 12 +----------- > drivers/firmware/efi/libstub/arm64-stub.c | 8 +++----- > 3 files changed, 4 insertions(+), 29 deletions(-) Acked-by: Will Deacon But I would really like to go a step further and rip out the block mapping support altogether so that we can fix non-coherent DMA aliases: https://lore.kernel.org/lkml/20200224194446.690816-1-hch@lst.de Will